Electro-optical device, electronic apparatus, method for forming a colored layer, and method for manufacturing the electro-optical device

ABSTRACT

The present invention provides an electro-optical device for displaying sharp color images at low cost. The electro-optical device can include a first substrate, a second substrate facing the first substrate, an electro-optical layer which is disposed between the first and second substrates and which includes electrophoretic particles and a dispersion medium, and a colored layer which is located at a position corresponding to the electro-optical layer and which includes at least one color element, wherein at least a part of the dispersion medium has substantially the same color as that of the color element.

This is a Divisional of application Ser. No. 10/200,446 filed Jul. 23,2002 now U.S. Pat. No. 6,862,128. The entire disclosure of the priorapplication is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to an electro-optical device, anelectronic apparatus, a method for forming a colored layer, and a methodfor manufacturing the electro-optical device.

2. Description of Related Art

Currently, among non-emissive displays, an electrophoretic displayutilizing the electrophoretic phenomenon is known. Electrophoresis is aphenomenon in which particles are caused to migrate by a Coulomb forcewhen a voltage is applied to a disperse system in which particles(electrophoretic particles) are dispersed in a liquid (dispersionmedium).

An electrophoretic display has a basic structure in which electrodesoppose each other with a predetermined distance therebetween, and theportion between the electrodes is filled with a disperse system. Whenpotential difference is given to the electrodes, charged electrophoreticparticles are attracted to either of the electrodes, depending on thedirection of the electric field. When a dispersion medium is coloredwith a dye, and the electrophoretic particles include a pigment,observers see the color of either the electrophoretic particles or thedispersion medium. When the electrodes are formed by patterning, imagescan be displayed by controlling the voltage applied to the electrodes.

SUMMARY OF THE INVENTION

Because of its qualities, the above electrophoretic display drawsattention as an alternative to a liquid crystal display. However, inorder to use the electrophoretic display as a display device forelectronic apparatuses, it is necessary to colorize the display.

The present invention has been made to solve the above problem, and anobject of the present invention to provide an electro-optical devicethat is capable of providing a sharp color display at low cost.

It is another object of the present invention to provide an electronicapparatus having the above electro-optical device.

It is another object of the present invention to provide a method forforming a colored layer adapted to electro-optical devices.

It is another object of the present invention to provide a method formanufacturing the electro-optical device.

The present invention can provide an electro-optical device having anelectro-optical layer including electrophoretic particles and adispersion medium, and a colored layer provided at the viewing side ofthe electro-optical layer. That is, the present invention provides acolor electro-optical device having the colored layer disposed on theviewing side of the electro-optical layer.

The present invention can also provide an electro-optical device furtherincluding a first substrate and a second substrate facing the firstsubstrate, wherein the electro-optical layer and the colored layer areplaced between the first and second substrates. According to the aboveconfiguration, it is not necessary to prepare separately a color filter,and the electro-optical device for displaying color images can beprovided at low cost.

The present invention provides an electro-optical device furtherincluding a first electrode provided on the first substrate and a secondelectrode provided on the second substrate, wherein the electro-opticallayer and the colored layer are placed between the first and secondelectrodes.

The present invention provides an electro-optical device furtherincluding a plurality of dot regions, wherein the colored layer includesa plurality of color elements having different colors, and each of theplurality of dot regions corresponds to at least one of the plurality ofcolor elements.

According to the above configuration, the electro-optical devicedisplays different colors for each of the dot regions.

The present invention provides an electro-optical device in which eachof the plurality of dot regions is separated by a partition. Accordingto the above configuration, since the dispersion medium in theelectro-optical layer is isolated for each dot region, unevendistribution of the electrophoretic particles does not arise, andtherefore the electro-optical device has high display quality andexcellent reliability.

The present invention provides the electro-optical device in which theelectro-optical layer further includes capsules for containing thedispersion medium and the electrophoretic particles. According to theabove configuration, since an area in which the electrophoreticparticles migrate is limited to the inside of the capsules, unevendistribution of the electrophoretic particles does not arise, andtherefore the electro-optical device has high display quality andexcellent reliability.

The present invention provides an electro-optical device in which theelectro-optical layer can include a plurality of types of the capsules,the colored layer includes the plurality of color elements havingdifferent colors, and each of the plurality of types of capsulescorresponds to at least one of the plurality of color elements.According to the above configuration, since at least one color elementis disposed for each capsule, uneven distribution of the electrophoreticparticles does not arise, and therefore the electro-optical device hashigh display quality and excellent reliability.

The present invention can provide an electro-optical device, in whichthe colored layer has conductivity. According to the aboveconfiguration, the colored layer having conductivity reduces thecapacitance formed in the colored layer by coloring material dispersedin the colored layer. Thus, the voltage applied to the electro-opticallayer to cause the electrophoretic particles to migrate is decreased, sothat the electro-optical device can be driven with low voltage.

The present invention can provide an electro-optical device including afirst substrate, a second substrate facing the first substrate, anelectro-optical layer including electrophoretic particles and adispersion medium, the electro-optical layer being placed between thefirst and second substrates, and a colored layer including at least onecolor element, the colored layer being located at a positioncorresponding to the electro-optical layer, wherein at least a part ofthe dispersion medium has substantially the same color as that of thecolor element.

According to the above configuration, since the colored layer located ata position corresponding to the electro-optical layer disposed betweenthe first and second substrates has substantially the same color as thatof the dispersion medium in the electro-optical layer, sharp colorimages can be displayed and the electro-optical device can be providedat low cost.

The present invention provides an electro-optical device in which thecolor elements included in the colored layer are dispersed in thedispersion medium. According to the above configuration, since thecolored layer is colored with the color elements for coloring thedispersion medium, the electro-optical device displays color imageswithout separately using a color filter and is thus provided at lowcost. The color patterns of the colored layer can be changed simply bychanging the colors of the color elements.

The present invention provides an electro-optical device furtherincluding a plurality of dot regions, in which the colored layerincludes a plurality of color elements having different colors. Each ofthe plurality of dot regions can correspond to at least one of theplurality of color elements, and in the dot regions, the dispersionmedium has substantially the same color as that of the color elementscorresponding to the dispersion medium. According to the aboveconfiguration, since each of the dot regions comprises the coloredlayer, the electro-optical device displays any images with desiredcolors.

The present invention provides the electro-optical device in which eachof the plurality of dot regions is separated by a partition. Accordingto the above configuration, since the dispersion medium in each of thedot regions partitioned by the partitions has any color, theelectro-optical device has dot regions each showing a different color.

The present invention provides an electro-optical device in which thefirst substrate has electrodes on the inside face thereof and thecolored layer is disposed between the electrodes and the electro-opticallayer.

The present invention can also provide an electro-optical device inwhich the colored layer has a member with a plurality of pores, thedispersion medium includes coloring material having the diameter thesame as or smaller than that of the pores, and the electrophoreticparticles have a diameter larger than that of the pores. According tothe above configuration, since only the coloring material contained inthe dispersion medium is dispersed to the colored layer side through thepores and the electrophoretic particles migrate only in the dispersionmedium, the migration of the electrophoretic particles in the dispersionmedium is not restricted, so that the electrophoretic device hasexcellent reliability.

The present invention provides an electro-optical device in which thecoloring material includes a dye. According to the above configuration,since the coloring material contains a dye, the coloring materialreadily moves in the dispersion medium and is readily distributed in thecolored layer.

The present invention provides an electro-optical device in which theelectro-optical layer further includes capsules containing thedispersion medium and the electrophoretic particles. According to theabove configuration, since the area in which the electrophoreticparticles migrate is limited to the inside of the capsules, thedistribution of the electrophoretic particles in the electro-opticallayer is uniform, so that the electro-optical device has excellentreliability.

The present invention can also provide an electro-optical device inwhich the electro-optical layer includes a plurality of types ofcapsules, the colored layer includes the plurality of color elementshaving different colors, each of the plurality of types of capsulescorresponds to at least one of the plurality of color elements, and inthe capsules, the dispersion medium has substantially the same color asthat of the color elements corresponding to the dispersion medium.According to the above configuration, since an electro-optical layercorresponding to each color element is controllable and the capsuleshave the same color as that of the colored layer, sharp color images canbe displayed.

The present invention provides an electronic apparatus having any one ofthe above-described electro-optical devices functioning as a displayportion. According to the above configuration, an electronic apparatushaving a display portion for displaying sharp color images can beprovided at low cost.

Additionally, the present invention can provide a method for forming acolored layer including the steps of changing the relative positionalrelationship between a porous member and a head discharging a material,and discharging the material onto the porous member, wherein thematerial includes a coloring material having a size smaller than that ofthe pores of the member. According to the above configuration, since thematerial containing the coloring material that can be dispersed in theporous member to color the member is arranged at an arbitrary positionon the porous member, the plurality of materials containing coloringmaterial having different colors can efficiently be placed.

Further, the present invention provides a method for forming a coloredlayer in which the coloring material includes a dye. According to theabove configuration, since the coloring material including a dye canreadily be dispersed in the porous member, the porous member isuniformly colored.

The present invention can provide a method for manufacturing anelectro-optical device having a plurality of dot regions, including thesteps of changing the relative positional relationship between a headdischarging a material and a substrate provided with porous memberscorresponding to the dot regions, and discharging the material onto theporous member from the head, wherein the material includes a coloringmaterial having a size smaller than that of pores of the member.

According to the above configuration, since the material is placed atany position on the porous member and the porous member is thus coloredwith the coloring material contained in the material to form the coloredlayer, an electro-optical device for displaying color images with thecolored layer can be efficiently manufactured.

The present invention provides a method for manufacturing anelectro-optical device in which the material includes electrophoreticparticles, and the electrophoretic particles have a diameter larger thanthat of the pores provided in the member. According to the aboveconfiguration, since the electrophoretic particles do not enter theporous member, the porous member does not prevent the electrophoreticparticles from migrating, so that the electro-optical device has a highdisplay quality and excellent reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numerals represent like elements, and wherein:

FIG. 1 is a perspective view showing a configuration of anelectrophoretic display according to a first embodiment of the presentinvention;

FIG. 2 is a plan view of the electrophoretic display shown FIG. 1;

FIG. 3 is a perspective view showing a configuration of anelectrophoretic display according to a second embodiment of the presentinvention;

FIG. 4 is a plan view of the electrophoretic display shown FIG. 3;

FIG. 5 is an enlarged sectional view showing the configuration of theelectrophoretic display shown FIG. 3;

FIG. 6 is a sectional view showing another configuration of theelectrophoretic display shown FIG. 3;

FIG. 7 is a sectional view showing another configuration of theelectrophoretic display shown FIG. 3;

FIG. 8 is a sectional view showing another configuration of theelectrophoretic display shown FIG. 3;

FIG. 9 is a graph showing the relationship between the displaybrightness and the contrast of the electrophoretic display shown FIG. 3;

FIG. 10 is a sectional view showing a microcapsule used in theelectrophoretic display according to a third embodiment of the presentinvention;

FIGS. 11A-11D are sectional views showing steps for manufacturing anelectrophoretic display according to the present invention;

FIGS. 12A-12D are sectional views showing other exemplary steps formanufacturing an electrophoretic display according to the presentinvention;

FIG. 13 is an illustration showing an exemplary method for ejecting thedispersion medium shown in FIG. 12C;

FIG. 14 is an illustration showing an exemplary electronic apparatusaccording to the present invention;

FIG. 15 is an illustration showing an exemplary electronic apparatusaccording to the present invention;

FIG. 16 is an illustration showing an exemplary electronic apparatusaccording to the present invention; and

FIG. 17 is an illustration showing an exemplary electronic apparatusaccording to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a perspective view schematically showing an active matrixelectrophoretic display, which is an electro-optical device of a firstembodiment according to the present invention. FIG. 2 is a plan view ofthe active matrix electrophoretic display shown in FIG. 1. FIG. 1 showsthe cross sectional structure taken along the line I—I of FIG. 2.

Referring to the above figures, in an electrophoretic display 10, anelectrophoretic layer (electro-optical layer) 11 is disposed between afirst substrate 1 and a second substrate 8. A colored layer 4 and commonelectrode 2 are disposed on the inside of the first substrate 1 (on theside of the electrophoretic layer 11) in that order, and an elementregion 7 having a plurality of pixel electrodes 7 a and the like isdisposed on the inside of the second substrate 8 (on the side of theelectrophoretic layer 11). On the side of the first substrate 1, thefirst substrate 1, the colored layer 4, and the common electrode 2 arelight transmitting. The outer face of the first substrate 1 functions asa display surface of the electrophoretic display 10. The secondsubstrate 8 having the element region 7 may further have variousperipheral devices, not shown, for controlling the element region 7. Thecommon electrode 2 is disposed on the side of the first substrate 1 andthe element region 7 is located on the side of the second substrate 8 inthis embodiment. However, the element region 7 may be located on theside of the first substrate 1.

The first substrate 1 can include, for example, a transparent glass ortransparent film substrate, having light-transmitting property. Thesecond substrate 8 does not necessarily have transparency and caninclude, for example, a glass or resin film substrate.

Referring to FIG. 1, the electrophoretic layer 11 has a dispersionmedium 5 and a plurality of electrophoretic particles 6 dispersedtherein. The dispersion medium 5 can include water; an alcohol solvent,such as methanol, ethanol, isopropanol, butanol, octanol, and methylcellosolve; esters such as ethyl acetate and butyl acetate; ketones suchas acetone, methyl ethyl ketone, and methyl isobutyl ketone; aliphatichydrocarbons such as pentane, hexane, and octane; alicyclic hydrocarbonssuch as cyclohexane and methylcyclohexane; aromatic hydrocarbons such asbenzene, toluene, and xylene; long-chain alkylbenzenes such ashexylbenzene, heptylbenzene, octylbenzene, nonylbenzene, decylbenzene,undecylbenzene, dodecylbenzene, tridecylbenzene, and tetradecylbenzene;hydrocarbon halides such as methylene chloride, chloroform, carbontetrachloride, and 1,2-dichloroethane; carboxylate; and other oils.These compounds can be used alone, or the mixture thereof furthercontaining a surfactant can also be used.

The electrophoretic particles 6 include organic or inorganic particles(polymer or colloid) having the property of migrating in the dispersionmedium due to electrophoresis caused by a potential difference. Forexample, one or more kinds of white pigments such as titanium oxide,hydrozincite, and antimony oxide can be used. Theses pigments mayfurther contain charge-controlling agents having particles includingelectrolytes, surfactants, metal soap, resins, rubber, oil, varnish, orcompounds; dispersants such as titanium coupling agents, aluminumcoupling agents, and silane coupling agents; lubricants; and stabilizingagents.

It should be understood that the combination of the dispersion medium 5and the electrophoretic particles 6 is not particularly limited, and itis preferable that the dispersion medium 5 and the electrophoreticparticles 6 have substantially the same density in order to avoid theprecipitation of the electrophoretic particles 6 by gravitation.

FIG. 2 is a plan view showing the configuration of the image displayingregion of a electrophoretic display according to the present embodiment.As shown, the image displaying region has a plurality of pixel portions17 (pixel electrodes 7 a and TFT elements 7 b) arranged in a matrix,data lines 70 a, and scanning lines 71 a. In the electrophoretic displayof this embodiment, each of a plurality of displaying units, which arearranged in a matrix and are included in the image-displaying region,includes one of the pixel electrodes 7 a functioning as transparentconductive layers and one of the TFT elements 7 b for controlling thecurrent supplied to the pixel electrodes 7 a, and each of the data lines70 a to which image signals are supplied is electronically connected toeach of the sources of the TFT elements 7 b. Image signals written onthe data lines 70 a are line-sequentially supplied or are supplied bygroup to the plurality of data lines 70 a neighboring each other.

Each of the scanning lines 71 a is electrically connected to one of thegates of the TFT elements 7 b, so that scanning signals areline-sequentially supplied to the plurality of scanning lines 71 aintermittently with predetermined timing. Each of the pixel electrodes 7a is electrically connected to each of the drains of the TFT elements 7b, so that image signals supplied from each data line 70 a are writtenat a predetermined timing by turning on each TFT element 7 b for apredetermined period. The image signals, having a predetermined level,written on each pixel electrode 7 a are held between the commonelectrode 2 and the pixel electrode 7 a for a given period. Electricallycharged particles are attracted to an electrode that is one of the pixelelectrode 7 a and the common electrode 2 and that has a polarityopposite to that of the charged particles, so that a grayscale can bedisplayed using the contrast between the color of the charged particlesand the color of the dispersion medium.

As shown in FIG. 2, a plurality of the pixel electrodes 7 a are arrangedin a matrix on an element substrate, and the data lines 70 a and thescanning lines 71 a extend along vertical and horizontal boundaries ofthe pixel electrodes 7 a. In this embodiment, each of the display units(dots) is the display region provided in an area surrounded by each ofthe data lines 70 a and each of the scanning lines 71 a, so that it ispossible to perform display in each of the display units, which arearranged in a matrix.

As shown in FIG. 2, a colored layer 4 has a configuration in which aplurality of colored portions (color elements) 4R, 4G, and 4B arearranged in a matrix in plan view, and the colored portions 4R, 4G, and4B are red, green, and blue, respectively. One pixel of theelectrophoretic display 10 according to the present embodiment includesthe colored portions 4R, 4G, and 4B, the pixel portions 17 of theelement region 7 located at positions opposing the colored portions, theelectrophoretic layer 11 placed between the colored portions and thepixel portions 17. That is, the electrophoretic display 10 of thisembodiment is capable of full color display, and each pixel shows one ofthe three primary colors (RGB). The common electrode 2 comprises atransparent conductive material such as ITO (indium tin oxide).

In the electrophoretic display 10 having the above configuration, anelectric field is formed between each of the pixel electrodes 7 alocated on the side of the second substrate 8 and the common electrode 2located on the side of the first substrate 1 to make the electrophoreticparticles 6 in the electrophoretic layer 11 migrate, so that a grayscaleis displayed in response to data signals supplied to the pixelelectrodes 7 a. That is, in the electrophoretic display 10 of thisembodiment, the dispersion of the electrophoretic particles 6 in theelectrophoretic layer 11 in the thickness direction is controlled usingthe intensity of the electric field applied to the electrophoretic layer11, so that the absorbance of light reflected by the electrophoreticparticles 6 is adjusted. As a result, the intensity of light reachingobservers can be changed.

As described above, in the electrophoretic display 10 of thisembodiment, since the colored layer 4 is placed between the firstsubstrate 1 and the second substrate 8, which face each other, sharpcolor images can be a displayed and low-cost production can be achievedbecause color filters are not separately required.

An electrophoretic display of a second embodiment according to thepresent invention will now be described with reference to FIGS. 3 and 4.FIG. 3 is a sectional view showing the configuration of anelectrophoretic display 20 of this embodiment and FIG. 4 is a partialplan view of the electrophoretic display shown in FIG. 3. FIG. 3 showsthe sectional structure taken along the line II—II shown in FIG. 4.

In the electrophoretic display 20, an electrophoretic layer(electro-optical layer) 31 is disposed between a first substrate 21 anda second substrate 28, a colored layer 24 and common electrode 22 aredisposed on the inside of the first substrate 21 (on the side of theelectrophoretic layer 31) in that order, and an element region 7 havinga plurality of pixel electrodes 7 a and the like is disposed on theinside of the second substrate 28 (on the side of the electrophoreticlayer 31). The first substrate 21, the colored layer 24, and the commonelectrode 22 are light transmitting on the first substrate 21 side. Theouter face of the first substrate 21 functions as a display surface ofthe electrophoretic display 20.

The first substrate 21 and the second substrate 28 may have the sameconfigurations as those of the first substrate 1 and the secondsubstrate 8 of the first embodiment shown in FIG. 1. The commonelectrode 22 disposed on the inside of the first substrate 21 caninclude a transparent material, such as ITO. The element region 7disposed on the inside of the second substrate 28 has the sameconfiguration as that of the other element region shown in FIG. 1. Inthis embodiment, the common electrode 22 is disposed on the side of thecolored layer 24, and the element region 7 may be disposed between thecolored layer 24 and the first substrate 21. In the latter case, pixelelectrodes 7 a in the element region 7 can include a transparentmaterial, such as ITO.

The electrophoretic layer 31 according to the present embodimentincludes the colored layer 24 disposed on the side of the firstsubstrate 21 and partitions 27 having a certain height in the thicknessdirection of the electrophoretic display 20 and forming lattice-work inplan view. Each region partitioned by the partitions 27 contains adispersion medium 25 and electrophoretic particles 6 in a sealed manner.In the electrophoretic display 20 of this embodiment, the regionpartitioned by the partitions 27 is referred to as a partitioned cell Cand each pixel corresponds to the partitioned cell C. In such aconfiguration, since the electrophoretic particles 26 dispersed in thedispersion medium 25 are allowed to migrate only inside the partitionedcell C, the uneven distribution of the particles and the formation ofagglomerations having the plurality of particles in the electrophoreticlayer 31 are effectively prevented. Thus, the quality of displayedimages is improved.

In this embodiment, one partitioned cell C corresponds to one pixel, anda plurality of colored portions and pixel portions 17 may be provided inone partitioned cell C.

As shown in FIG. 4, the plurality of pixel electrodes 7 a are arrangedin a matrix on an element substrate, and the data lines 70 a and thescanning lines 71 a extend along vertical and horizontal boundaries ofthe pixel electrodes 7 a. In this embodiment, each of the display units(dots) are the display region provided in an area surrounded by each ofthe data lines 70 a and each of the scanning lines 71 a, so that it ispossible to perform display in each of the display units arranged in amatrix.

The partitions 27, shown by the diagonally shaded areas in FIG. 4, arelocated to overlap in a plan view with the data lines 70 a and thescanning lines 71 a, which are wires, and the TFT elements 7 b. As shownin FIG. 3, each of the partitions 27 are located between the pixelelectrodes 7 a so as to partition the color display units correspondingto respective colors of color filters, which are red (R), green (G), andblue (B).

The dispersion medium 25 of the electrophoretic layer 31 according tothe present embodiment is colored with coloring material containing adye. Since the colored layer 24 is also colored with the same coloringmaterial, the dispersion medium 25 and the colored layer 24 havesubstantially the same color. The configuration of the electrophoreticlayer 31 will now be described in detail with reference to FIG. 5. FIG.5 is an enlarged sectional view showing the configuration of theelectrophoretic layer 31 shown in FIG. 3.

In the electrophoretic layer 31 shown in FIG. 5, the colored layer 24,which is placed at the upper area in the figure, is immersed in thedispersion medium 25, in which electrophoretic particles 26 and coloringmaterial 30 are dispersed. The colored layer 24 can include a porousbody having a large number of pores 24 a, and the dispersion medium 25and the coloring material 30 are dispersed in the colored layer 24through the pores 24 a to color the colored layer 24. Since the pores 24a have a diameter smaller than that of the electrophoretic particles 26,the electrophoretic particles 26 cannot enter the colored layer 24including the porous body and can migrate only in the dispersion medium25 in the partitioned cell.

The electrophoretic particles 26 may include, for example, a whitepigment such as titanium oxide, hydrozincite, and antimony oxide.

The porous material for the colored layer 24 may include, for example,porous glass. The porous glass may be prepared by the followingmanufacturing method. NaO—B₂O₃—SiO₂ glass is prepared from SiO₂ (silicasand), H₃BO₃ (boric acid), and Na₂CO₃ (soda ash), which are rawmaterials, by a well-known melting process. When the resulting glass isthen heat-treated at several hundred degrees centigrade, a SiO₂ richphase and a Na₂O—B₂O₃ rich phase are formed in the glass on a scale ofseveral nanometers due to spinodal decomposition. The phase separatedglass is immersed in an acidic solution to dissolve only the Na₂O—B₂O₃rich phase and porous glass having a SiO₂ framework is then obtained.The porous glass obtained by this method has perforating pores extendingfrom the surface to the inner part. Thus, when the porous glass is usedas the colored layer 24, a dye easily permeates the inside. The porediameter of the porous glass is readily controlled by the thermaltreatment conditions.

Other porous material may be porous silicon, porous ceramics, porousgels prepared by a sol-gel method, or the like. Since these porousmaterials contain an inorganic substance as a main component,deterioration by ultraviolet radiation rarely occurs and excellentweather resistance is obtained. Thus, a long-life electrophoreticdisplay can be achieved.

There can be an advantage in that the coloring material in thedispersion medium 25 supplements the material coloring the colored layer24.

The colored layer 24 may include any one of the above materials as theporous material therefor, and preferably include one having therefractive index the same as or close to that of the dispersion medium25. When both refractive indexes are substantially the same, thescattering caused by a differential between the different refractiveindexes is reduced to achieve a display having high contrast and colorpurity.

While the colored layer 24 including a porous material is describedabove, another colored layer used in an electrophoretic displayaccording to the present invention may include a colorable materialwhich is readily colored by the permeation of a dye. FIG. 6 is asectional view showing the configuration of the electrophoretic layer 31having another colored layer 34 including such a colorable material. Asshown in the figure, the colored layer 34 includes the colorablematerial and the colored layer 34 is colored with coloring materialcontained in the dispersion medium 25 and thus has substantially thesame color as that of the dispersion medium 25. The colorable materialmay include, for example, a polyimide resin, a colorable resist preparedby adding a bichromate into a water-soluble polymer such as gelatin,casein, and the like. When the colored layer 34 includes such acolorable material, it is preferable that the electrophoretic particles26 do not enter the colored layer 34.

The colored layers 24 and 34 according to the present embodiment mayhave conductivity. In such a configuration, the electrophoretic layer 31can be driven with a low voltage. The configuration will now bedescribed with reference to FIG. 7. FIG. 7 is a sectional view showingthe configuration of the electrophoretic layer 31 including a coloredlayer 44 having conductivity. A circuit for the electrophoretic layer 31is also shown in FIG. 7.

Electrodes for driving the electrophoretic particles 26 are disposed onboth outer faces (upper and lower faces in the figure) of theelectrophoretic layer 31. If the colored layer 44 does not haveconductivity, a region of the electrophoretic layer 31 containing theelectrophoretic particles 26 functions as a capacitor C1 and the coloredlayer 44 functions as another capacitor C2. However, since the coloredlayer 44 has conductivity in this configuration, the colored layer 44functions as a resistance, which is indicated with R in the circuitdiagram, and a path bypassing the capacitor C2 is formed. Accordingly,the capacitance of the electrophoretic layer 31 is substantially reducedand the electrophoretic particles 26 can thus be driven with a lowvoltage.

As shown in a sectional view in FIG. 8, in the electrophoretic layer 31according to the present invention, the partitioned cell C is furtherpartitioned into two parts with a translucent film 53. When theelectrophoretic particles 26 are situated only in the one part (lowerpart in the figure) of the two, the other part in which theelectrophoretic particles 26 are not situated may function as a coloredlayer 54. The dispersion medium 25 and the coloring material 30 passthrough the translucent film 53 while the electrophoretic particles 26cannot pass through the translucent film 53. The materials for thetranslucent film 53 are not limited as long as the materials havelight-transmitting property, and may include polyimides and silicone.

In the configurations shown in FIGS. 5 to 8, the electrophoretic displayof this embodiment has a colored layer in the electrophoretic layer 31,and thus provides sharp color images without separately requiring acolor filter. Accordingly, the present invention provides anelectrophoretic display providing high quality images at low cost.

The electrophoretic display 20 of this embodiment having the aboveconfiguration provides a grayscale for each partitioned cell C.

The principle of the light modulation is described below. The intensityI of incident light is resolved into three components (IR, IG, and IB)corresponding to the wavelengths of the three primary colors. This isexpressed by formula (1) as follows:I=IR+IG+IB  (1)

While full-color display requires controlling the three colors, apartitioned cell C having a monochrome colored portion 24R is describedherein. When colors other than red are absorbed by a colored portion24R, the reflective intensity (Irefon) in a bright (ON) state is definedas the product of the red light transmittance (Tfr) of the coloredportion 24R and the reflectance (Rr) of the electrophoretic particlesand is expressed by formula (2), wherein Ir represents the intensity ofthe incident light, as follows:Irefon=Ir·Tfr ² ·Rr  (2)

The reflective intensity (Irefoff) in a dark (OFF) state is defined asthe product of the reflectance of each component, the transmittance (Tr)per unit length of a solvent, and the optical path length (Lr) and isexpressed by formula (3) as follows:Irefoff=Ir·Tfr ² ·Tr ² Lr ² ·Rr  (3)

FIG. 9 shows the relationship between cell length, brightness, andcontrast, wherein the brightness and the contrast are obtained using theabove formulas. The number of each point in the graph shown in FIG. 9 isdescribed in Table 1. The brightness and the contrast shown in thefigure and the table are calculated values based on the assumption thatthe colored portion 24R and the dispersion medium 25 both have atransmittance of 90% per 1 μm. In the electrophoretic display shown inFIG. 3, the state in which the electrophoretic particles 26 touch theinner face of the colored layer 24 (the state in which mostelectrophoretic particles 26 have moved to the side of the observer)corresponds to a cell thickness of 1 μm, and the brightness is 81%. Ifthe state in which most electrophoretic particles 26 have moved to theside of the element region 7 means that the cell thickness is 20 μm, thebrightness depends on the reflective intensity of the dispersion medium25 and is 1.5%. Thus, the electrophoretic display having this conditionhas a contrast of about 55.

TABLE 1 Cell Thickness Brightness Contrast  0 μm  100%  1 μm 81.0% 1.0 2 μm 65.6% 1.2  3 μm 53.1% 1.5  4 μm 43.0% 1.9  5 μm 34.9% 2.3  6 μm28.2% 2.9  7 μm 22.9% 3.5  8 μm 18.5% 4.4  9 μm 15.0% 5.4 10 μm 12.2%6.7 11 μm  9.8% 8.2 12 μm  8.0% 10.2 13 μm  6.5% 12.5 14 μm  5.2% 15.515 μm  4.2% 19.1 16 μm  3.4% 23.6 17 μm  2.8% 29.1 18 μm  2.3% 36.0 19μm  1.8% 44.4 20 μm  1.5% 54.8 21 μm  1.2% 67.7 22 μm  1.0% 83.5 23 μm 0.8% 103.1 24 μm  0.6% 127.3 25 μm  0.5% 157.2

In the second embodiment, the electrophoretic layer 31 has thepartitions 27 to limit the area where the electrophoretic particles 26are allowed to migrate in the electrophoretic layer 31, so that theuniformity of the distribution of the electrophoretic particles 26 isimproved.

A microcapsule 60 shown in FIG. 10 may be used instead of thepartitioned cell C shown in FIG. 3. FIG. 10 is a sectional view showinga microcapsule 60 applicable to an electrophoretic layer according tothe present invention. The microcapsule 60 includes outer and innercapsule film 61 and 62, respectively, which form a double film, adispersion medium 25, and electrophoretic particles 26, both of whichare situated in the space surrounded by the inner capsule film 62. Thedispersion medium 25 includes a coloring material, as described in theabove embodiments.

In the outer and inner capsule films 61 and 62, respectively, which forma double film, the outer capsule film 61 functions as a protective filmand can include a transparent natural polymer such as gelatin or gumarabic or a synthetic polymer such as carboxymethyl cellulose,carboxyethyl cellulose, polyvinyl alcohol, nylon, polyurethane,polyester, epoxy, or melamine-formalin. The inner capsule film 62comprises the same colorable material as that of the colored layer 34shown in FIG. 6. The inner capsule film 62 is colored with a coloringmaterial contained in the dispersion medium 25 covered by the innercapsule film 62. Thus, when the plurality of microcapsules 60 arearranged in a matrix on the pixel electrodes 7 a of the element region 7shown in FIG. 3, the same function as that of the electrophoretic layer31 having the partitioned cells C partitioned by the partitions 27 canbe obtained.

In the electrophoretic display including the microcapsules 60 of thisembodiment, since the inner capsule film 62 of each microcapsule 60shown in FIG. 10 functions as a colored layer, sharp color images can bedisplayed without separately requiring a color filter and a colorelectrophoretic display can thus be provided at low cost.

As an exemplary method for manufacturing an electrophoretic displayaccording to the present invention, a method for manufacturing theelectrophoretic display shown in FIG. 3 will now be described withreference to FIG. 11. FIGS. 11A to 11D are sectional views showingmanufacturing steps in a manufacturing method according to the presentinvention. In this embodiment, manufacturing steps of an electrophoreticlayer (electro-optical layer) according to the present invention aredescribed in detail.

When the electrophoretic display shown in FIG. 3 is manufactured by amethod according to the present invention, a common electrode, notshown, is first formed on the first substrate 21. As shown in FIG. 11A,the colored layer 24 including the colored portions 24R, 24G, and 24Band banks 24M for partitioning the colored portions is then formed. Thebanks 24M function as bases of the partitions 27, described below, andmay comprise the same material as the partitions 27. The colored layer24 may be formed by a known method for manufacturing a color filter. Thecolored layer 24 may be colored with a dye.

As shown in FIG. 11B, the partitions 27 are formed on the banks 24M soas to have a predetermined height. The height of the partitions 27corresponds to that of the cells in the electrophoretic display and is5-50 μm. When the partitions 27 are formed, a resin which is hardened byirradiation with UV, heating, condensation, or addition polymerizationis used, such a resin is gradually deposited on the banks 24M by usingan ink jet unit, and the deposited resin having a predetermined heightis then set.

As shown in FIG. 11C, each region (which corresponds to the partitionedcell C in FIG. 3) partitioned by the partitions 27 is then filled with adispersion medium 25 and electrophoretic particles 26. The dispersionmedium 25 may or may not contain a coloring material. When thedispersion medium 25 contains no coloring material, the colored layer 24is impregnated in advance with a concentrated dye in the step of formingthe colored layer 24 and the partitioned regions are then filled withthe dispersion medium 25 in a state that the dye does not get dried, sothat the dye in the colored layer 24 leaches into the dispersion medium25 to color the dispersion medium 25.

As shown in FIG. 11D, a seal 32 is provided on the upper end of eachregion filled with the dispersion medium 25 and the electrophoreticparticles 26 to form the electrophoretic layer according to the presentinvention. The seal 32 can include a conductive material such as a resincontaining carbon or metal fibers. In such a case, since the seal 32functions as a common electrode, cost reduction can be achieved by theuse of common members. Thus, weight-saving and thickness-reduction ofthe electrophoretic display can also be achieved. When the seal 32 isused as a common electrode, it is not necessary to provide anothercommon electrode on the first substrate 21 before forming the coloredlayer shown in FIG. 11A. When the seal 32 can include an insulatingmaterial, ion implantation may be performed for the seal 32 afterfinishing sealing to provide conductivity to the seal 32.

In the above description, a method for forming the colored layer 24 by aconventional process for forming a color filter is mentioned. In theelectrophoretic display according to the present invention, the coloredlayer 24 may be formed using a porous material and may then beimpregnated with a coloring material to be colored. This method will nowbe described with reference to FIG. 12.

As shown in FIG. 12A, a plurality of porous portions 24 b and banks 24Mfor partitioning the porous portions 24 b at predetermined intervals areformed on a first substrate 21 including glass, a resin film, or thelike. The porous portion 24 b may comprise porous glass, porous silicon,or the like as describe above and the banks 24M may include a resin orthe like.

As shown in FIG. 12B, partitions 27 are formed on the banks 24M so as tohave a predetermined height. The method for forming the partitions 27may be the same as that described above. As shown in FIG. 12C, eachregion (partitioned cell C) partitioned by the partitions 27 is thenfilled with a dispersion medium 25 and electrophoretic particles 26. Inthis step, the dispersion medium 25 contains a coloring material, theporous portions 24 b are colored with the coloring material in thedispersion medium 25 to have a predetermined color, and the coloredlayer 24 is then completed. FIG. 13 shows that an ink jet unit processis used in this step. As shown in FIG. 13, ink jet units 71-73 eachstore solution containing the dispersion medium 25 including a coloringmaterial corresponding to R, G, or B. Droplets 70 are ejected from theink jet units 71-73 into each region partitioned by the partitions 27 tocolor the porous portions 24 b with the coloring material in thedroplets 70, and colored portions 24R, 24G, and 24B having each colorare then formed in sequence. In this method, since a previously coloredlayer is not formed but the colored layer 24 is formed by fillingdispersion medium 25, a colored layer having various color patterns canbe formed and the degree of flexibility in the manufacturing method isthus increased. Furthermore, since the colored layer 24 is formed byejecting drops of the dispersion medium 25, the number of the steps canbe reduced, hence, the production cost is reduced while the yield isincreased.

As shown in FIG. 12D, the regions filled with the dispersion medium 25and the electrophoretic particles 26 are sealed with seals 32 to obtaina electrophoretic layer according to the present invention.

In the manufacturing method of this embodiment, only the steps forforming the electrophoretic layer including the colored layer 24 aredescribed. It should be understood that a method for manufacturing othermembers, for example, an element region 7, is not limited, and othermethods for manufacturing switching elements may also be used withoutdeparting from the spirit and scope of the present invention.

In this embodiment, the porous portions 24 b are formed and thepartitions 27 are then formed. However, the partitions 27 may beprovided in-advance on the first substrate 21 to form the porousportions 24 b by applying a porous material onto the first substrate 21partitioned by the partitions 27 or by ejecting the porous material withan ink jet unit.

An electro-optical device according to the present invention isapplicable to various electronic apparatus having a display portion.Exemplary applications of electronic apparatuses having anelectrophoretic display in the above embodiments will now be described.

An exemplary mobile (portable) personal computer having anelectrophoretic display according to the present invention will now bedescribed. FIG. 14 is a perspective view showing the configuration ofthe above personal computer. The personal computer 1200 has a displayportion 1201 that is an electrophoretic display according to the presentinvention. The personal computer 1200 has a main body 1202 including akeyboard 1203.

An exemplary mobile phone having an electrophoretic display according tothe present invention will now be described. FIG. 15 is a perspectiveview showing the configuration of this mobile phone. The mobile phone1300 has a small display portion 1301 that is an electrophoretic displayaccording to the present invention. The mobile phone 1300 includes aplurality of operating buttons 1302, a ear piece 1303, and a mouth piece1304.

An exemplary electronic sheet having an electrophoretic displayaccording to the present invention will now be described. FIG. 16 is aperspective view showing the configuration of this electronic sheet. Theelectronic sheet 1400 has a display portion 1401 that is anelectrophoretic display according to the present invention. Theelectronic sheet 1400 includes a main body 1402 having a rewritablesheet having the same texture and flexibility as that of conventionalpaper.

FIG. 17 is a perspective view showing the configuration of an electronicnotebook. The electronic notebook 1500 has a plurality of the boundelectronic sheets 1400 shown in FIG. 16 and a cover 1501 sandwiching theelectronic sheets 1400. The cover 1501 has, for example, a display-datainput means, not shown, for inputting display-data transmitted from anexternal device. Thus, displayed contents can be changed or updatedaccording to the display-data while the electronic sheets are bound.

In addition to the above examples, other applications include liquidcrystal television, a video tape recorder with a viewfinder or amonitor, a car navigation system, a pager, an electronic notebook, aportable calculator, a word processor, a workstation, a picture phone, aPOS terminal, devices having a touch panel, and the like. Anelectro-optical device according to the present invention is applicableto a display portion for such electronic apparatuses.

As described above in detail, an electro-optical device according to thepresent invention can include a first substrate, a second substratefacing the first substrate, an electro-optical layer which is disposedbetween the first and second substrates and which includeselectrophoretic particles and a dispersion medium, and a colored layerwhich is located so as to correspond to the electro-optical layer andwhich includes at least one color element, wherein at least a part ofthe dispersion medium has substantially the same color as that of thecolor element. Thus, sharp color images can be displayed and a low-costelectro-optical device can be provided.

While this invention has been described in conjunction with the specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, preferred embodiments of the invention as set forth hereinare intended to be illustrative not limiting. There are changes that maybe made without departing from the spirit and scope of the invention.

1. An electro-optical device, comprising: a first substrate; a secondsubstrate facing the first substrate; an electro-optical layer includingelectrophoretic particles and a dispersion medium, the electro-opticallayer being placed between the first and second substrates; a coloredlayer being disposed between the first substrate and the electro-opticallayer; and an element layer including at least a thin film transistor,the element layer being disposed between the electro-optical layer andthe second substrate.
 2. The electro-optical device according to claim1, further comprising: an electrode provided on the first substrate, thefirst substrate, the colored layer and the electrode havingtranslucency.
 3. The electro-optical device according to claim 1,further comprising: a plurality of dot regions, the colored layerincluding a plurality of color elements having different colors, andeach of the plurality of dot regions corresponding to at least one ofthe plurality of color elements.
 4. The electro-optical device accordingto claim 3, each of the plurality of dot regions being separated by apartition.
 5. The electro-optical device according to claim 1, theelectro-optical layer further including capsules that contain thedispersion medium and the electrophoretic particles.
 6. Theelectro-optical device according to claim 5, the electro-optical layerincluding a plurality of types of the capsules, the colored layerincluding a plurality of color elements having different colors, andeach of the plurality of types of the capsules corresponding to at leastone of the plurality of color elements.
 7. The electro-optical deviceaccording to claim 1, the colored layer having conductivity.
 8. Anelectro-optical device, comprising: a first substrate; a secondsubstrate facing the first substrate; an electro-optical layer includingelectrophoretic particles and a dispersion medium, the electro-opticallayer being placed between the first and second substrates; a coloredlayer being disposed between the first substrate and the electro-opticallayer; and an element layer including at least a thin film transistor,the element layer being disposed between the first substrate and theelectro-optical layer.
 9. The electro-optical device according to claim8, further comprising: at least a pixel electrode being included in theelement layer, the first substrate, the colored layer and the pixelelectrode having translucency.
 10. An electro-optical device,comprising: a first substrate; a second substrate facing the firstsubstrate; an electro-optical layer including electrophoretic particlesand a dispersion medium, the electro-optical layer being placed betweenthe first and second substrates; a colored layer being disposed betweenthe first substrate and the electro-optical layer, the colored layerincluding at least one color element; and an element layer including atleast a thin film transistor, the element layer being disposed betweenthe electro-optical layer and the second substrate, at least a part ofthe dispersion medium having substantially a same color as that of thecolor element.
 11. The electro-optical device according to claim 10, thecolor elements included in the colored layer being dispersed in thedispersion medium.
 12. The electro-optical device according to claim 10,further comprising: a plurality of dot regions, the colored layerincluding a plurality of color elements having different colors, each ofthe plurality of dot regions corresponding to at least one of theplurality of color elements, and in the dot regions, the dispersionmedium having substantially the same color as that of the color elementscorresponding to the dispersion medium.
 13. The electro-optical deviceaccording to claim 12, each of the plurality of the dot regions beingseparated by a partition.
 14. The electro-optical device according toclaim 10, the first substrate having electrodes on an inside facethereof, and the colored layer being disposed between the electrodes andthe electro-optical layer.
 15. The electro-optical device according toclaim 12, the colored layer having a member with a plurality of pores,the dispersion medium including coloring material having a diameter thesame as or smaller than that of the pores, and the electrophoreticparticles have a diameter larger than that of the pores.
 16. Theelectro-optical device according to claim 15, the coloring materialincluding a dye.
 17. The electro-optical device according to claim 12,the electro-optical layer further including capsules containing thedispersion medium and the electrophoretic particles.
 18. Theelectro-optical device according to claim 17, the electro-optical layerincluding a plurality of types of the capsules, the colored layerincluding the plurality of color elements having different colors, eachof the plurality of types of capsules corresponding to at least one ofthe plurality of color elements, and in the capsules, the dispersionmedium having substantially the same color as that of the color elementscorresponding to the dispersion medium.
 19. An electro-optical device,comprising: a first substrate; a second substrate facing the firstsubstrate; an electro-optical layer including electrophoretic particlesand a dispersion medium, the electro-optical layer being placed betweenthe first and second substrates; a colored layer being disposed betweenthe first substrate and the electro-optical layer, the colored layerincluding at least one color element; and an element layer including atleast a thin film transistor, the element layer being disposed betweenthe first substrate and the electro-optical layer, at least a part ofthe dispersion medium having substantially a same color as that of thecolor element.
 20. The electro-optical device according to claim 19,further comprising: at least a pixel electrode being included in theelement layer, the first substrate, the colored layer and the pixelelectrode having translucency.
 21. An electronic apparatus comprisingthe electro-optical device according to claim 1 functioning as a displayportion.
 22. An electronic apparatus comprising the electro-opticaldevice according to claim 10 functioning as a display portion.
 23. Anelectronic apparatus comprising the electro-optical device according toclaim 19 functioning as a display portion.